A Microarray Immunoassay for Serum Thyrotropin and Thyroglobulin Using Antibodies Immobilized on Track-Etched...

Serum thyroglobulin (Tg) and thyroid stimulating hormone (TSH) measurements have evolved as important analytes for monitoring the prognosis of patients with differentiated thyroid cancer, post-thyroidectomy. Individual analyte immunoassay is the current practice in clinical pathology, but the simultaneous assay for all relevant analytes for a given disease, can reduce assay costs, improve patient compliance and give the clinician more information for an unequivocal diagnosis. Microarray immunoassay (MI) can achieve this goal and, hence, we have developed and validated a immuno-radiometric MI for quantitation of serum TSH and Tg by using highly micro-porous polycarbonate (PC) track-etched membranes (TEM) to immobilize the monoclonal anti-TSH and polyclonal anti-Tg antibodies in ~1 mm diameter spots. Non-competitive immunoassays were performed using mixture of ¹²⁵I labeled monoclonal anti-TSH and anti-Tg antibodies. Phosphorimager was used to quantify the bound radioactivity. TSH and Tg were detected with detection limit of 0.07 µIU/ml and 0.13 ng/ml respectively, which is lower than the clinically required cut-off level. The assay showed: acceptable intra-assay precision within 20 % and recovery in the range of 76-111.2 %. MI compared well with the established immunoradiometric assay (IRMA) with r = 0.98, p < 0.01 (n = 41). No cross-reactivity was seen between the immobilized antibodies. Although two hormones are addressed in this report, MI using PC TEM and isotopic/non-isotopic tracers has the potential for highly automated multiplexed analysis.